The present invention relates to novel, curable carboxyfunctional silicone compositions. Said compositions are useful, in the cured state, as tough, protective, easily cleaned coatings for substrates.
Silicone coatings are in general quite well known. Pertinent to the present invention among such silicone coatings are those described in U.S. Pat. No. 4,322,518, issued Mar. 30, 1982 to J. Blizzard, and assigned to the assignee of the present invention. Said U.S. Patent describes compositions comprising: (1) certain liquid copolymeric organopolysiloxanes comprising SiO.sub.4/2 units, silicon-bonded hydroxyl radicals and/or silicon-bonded hydride radicals; and (2) a polydiorganosiloxane in which the organic radical substituents are monovalent hydrocarbon radicals, with each of the molecules of said polydiorganosiloxane containing at least two vinyl radicals or silicon-bonded hydroxyl radicals.
While coatings based on silicones having monovalent hydrocarbon radicals have enjoyed great success, said coatings have a marked tendency to soil or pick up dirt. Moreover, said coatings tend to retain dirt even upon rinsing with water. Such soiling behavior presents obvious disadvantages for some applications, such as applications in which coated articles find use outdoors or in heavy soiling industrial, agricultural, or residential environments.
Silicone coatings in which some or all of the substituents are not monovalent hydrocarbon radicals are also known. For example, silicone coatings comprising carboxyacid functional silicones are known. U.S. Pat. No. 4,011,362, issued Mar. 8, 1977, discloses metal substrates coated with a composition consisting essentially of a carboxyacid functional silicone and polydimethylsiloxane.
Other curable compositions comprising carboxyfunctional silicones are known. For example, U.S. Pat. No. 3,047,528 issued July 31, 1962, discloses carboxyacid functional silicone compositions curable to elastomers. Said compositions also include fillers, and polyvalent metal compound curing agents.
While the coatings of U.S. Pat. No. 4,011,362 provide excellent release surfaces for metal substrates, said coatings do not possess the strength and toughness needed for many applications. Said coatings cannot be successfully applied to a substrate other than as a relatively thin film, such as 0.025 mm or less.
The filled compositions of U.S. Pat. No. 3,047,528, on the other hand, are difficult if not impossible to apply as a coating less than 0.25 mm thick on a substrate.
Thus it would be beneficial to provide a carboxyfunctional silicone coating material capable of being applied to a substrate as a moderate to thick film, i.e. from about 0.025 mm to 0.25 mm thick. It would also be beneficial if the subsequently cured film could have a high degree of toughness and strength.